[剑指offer] 34. 第一个只出现一次的字符

class Solution
{
  public:
    int FirstNotRepeatingChar(string str)
    {
        int len = str.size();
        if (len == 0)
            return -1;
        map<char, int> mapping;

        for (auto c : str)
            mapping[c]++;

        for (int i = 0; i < len; i++)
        {
            if (mapping[str[i]] == 1)
                return i;
        }
        return -1;
    }
};